Automatic ionization chamber



Dec. 6, 1960 H. V. NEHER ET AL AUTOMATIC IONIZATION CHAMBER Filed April16, 1956 TIME BETWEEN DISCHAEGES SECS. i; u\

APPLIED POTENTIAL T0 SHIELD I4AND FIBEEZA' INVENTOR5 Heme) Wcroe Nev/5eBY '44 /v Eda/v 8729/ United States ate AUTOMATIC IONIZATION CHAlVlBERHenry Victor Neher and Alan R. Johnston, both of 1201 E. California St.,Pasadena, Calif.

Filed Apr. 16 1956, Set. No. 578,454 Claims. (Cl. 250-83.6)

This invention relates to automatic ionization chambers and included inthe objects of this invention are:

First, to. provide an automatic ionization chamber which is animprovement in the automatic ionization chamber' is directed to theaccompanying drawings in which:

Figure 1 is a fragmentary, partial elevational, partial sectional viewof the automatic ionization chamber.

Figure 2 is an enlarged fragmentary, transverse sectional view takenthrough 22 of Figure 1 with the surrounding shell of the ionizationchamber removed.

Figure 3 is a transverse, sectional view through 3--3 of Figure 2.

Figure 4 is a transverse, sectional view through 44 of Figure 2.

Figure "5 is a diagrammatical view showing the electrical connectionsimmediately associated with the ionization chamber.

Figure 6 is a graph or chart to illustrate the lack of influence ofchange in voltage on the operation of the ionization chamber.

The automatic ionization chamber includes a shell or envelope 1 which ispreferably spherical in form and constructed of metal or of any othersuitable material having a conductive coating. The shell 1 is providedwith a mouth 2 having a flange 3 which co-acts with a clamp ring 4 andsuitable screws to secure the margin of a terminal base 5. The terminalbase forms the lower end of a mounting unit 6 which projects into themouth of the shell 1. A seal ring 7 is provided between the flange 3 andthe margins of the terminal base 5.

The mounting unit 6 includes a glass seal 8 centrally disposed in theterminal base 5. Leads 9 extend through the seal, the outer extremitiesof which are connected to terminals 10 suitably supported in aninsulating memger 11 forming the lower extremity of the terminal ase 5.

The inner end ofthe mountingunit 6 supports-an outer shield ,12 which iscylindrical in form and projects into ;the .Shfillpr envelope 1. Theinner extremity of the shield ,1; 2,is clgsed except for a centralaperture .13. Supported .withintheouter shield 12 is an innerorelectrostatic shield 14 which is also cylindrical and closed at its.inner end except for anaperture .15 which. is co-axial with theaperture13. The inner or electrostatic shield 2,953,589 fiatented Dec. 6, 196014 is supported by extensions 9a of several of the leads 9 (in theconstruction illustrated, three of such extensions 9a are provided)which extend upwardly or inwardly from the glass seal 8. Theelectrostatic shield is centered relative to the outer shield 12 bymeans of glass or ceramic spacer tubes 16 held in place by tabs 17offset outwardly from the electrostatic shield and inserted in the endsof the tubes 16.

The mounting unit 6 includes a supporting plate 18 disposed within thelower end of the outer shield 12 and spaced from the lower end of theelectrostatic shield 14. The supporting plate 18 is provided withperipheral apertures which clear the leads 9. Centered in the plate 18is a socket member 19 which receives the lower end of quartz rod 20. Asuitable cement 21 secures the quartz rod within the socket member. Byway of example, the socket member may be formed of silver and a silverchloride cement may be employed.

The quartz rod 20 extends co-axially with respect to the outer shield 12and inner or electrostatic shield 14 and projects through the apertures15 and 13. The extended portion of the quartz rod 20 is plated orotherwise coated with metal, as indicated by 22, to form a conductivesurface. The protruding coated rod 20 func tions as an ion collector.The metal coated portion extends into the electrostaticshield 14. Fusedto the quartz rod 20 is an L-shaped arm 23 also formed of quartz andwhich includes a portion extending parallel with the quartz rod 20. Theupper extremity of the arm 23 tapers virtually to a point to form afiber 24 of extremely small diameter. The fiber 24 is bent horizontallyand positioned so that it may flex to and from contact with the metalcoated side of the quartz rodion collector 20 and, when connected with asource of potential, forms an element for recharging the ion collectorwhenever the potential of the ion collector has fallen to apredetermined value. The fiber 24 and adjacent portion of the arm 23 iscoated with metal as indicated by 25 to provide a conductive surface.The metal coating 25 is electrically connected to a wire 26 which inturn is connected to an extension 9b of one of the leads 9 whichprojects upwardly through a suitable aperture in the supporting plate18.

In use, only three of the terminals 10 are employed; namely, theterminal connected with the lead having the extension 9b, one of theterminals having the extension 9a, and one of the remaining terminals isconnected to the plate 18 or otherwise grounded by a lead 1c.

Reference is directed to Figure 5. The electrostatic shield 14 is placedat a high potential relative to the outer shield 12 and seal 1, theouter shield and seal being grounded. This terminal is connected througha resistor to the terminal connected with the lead extension 912.

' Under the conditions of operation, the voltage drop across theresistance 27 is negligible so that the electrostatic shield isvirtually the same potential as the fiber 24. The fiber is connectedthrough its terminal and a condenser 28 to a suitable amplifier such asshown in the aforementioned Patent 2,617,044 or other conventional typeof amplifier.

Operation of the automatic ionization chamber is as follows:

The ionization chamber formed by the shell 1 is filled with argon ofhigh purity to a pressure of several atmospheres. A pressure of eightatmospheres has been found satisfactory. The argon gas is ionized by theartificial or by cosmic radiation to which-the instrument is exposed.The projecting plated portion 22 of the quartz rod 21) forms an ioncollector for the ion charges fQlmed inthe argon gas.

Assuming an initially charged state of the collector element, the fiber2,4 occupies a repelled position shown 3 by solid lines in Figure 4. ioncharges resulting from ionization of the argon gas within the ionizationchamberformed by the shell 1 are attracted to and cumulatively reducethe potential of the ion collector 20. The apparatus is pre-designed toreceive from 10,000 to 50,000 ion charges before discharging the ioncollector sufiiciently to cause contact by the fiber or charging element24.

When the potential of the ion collector 22 drops to a value to which theelectrostatic element or fiber 24 touches it, current flows from thefiber 24 on to the ion collector rod 20, thereby lowering the potentialof the fiber and with it the potential at the input of the amplifierwhich is connected to the fiber through the condenser 28. This potentialdrop due to the mechanical contact of the fiber and collector occurs ina very short time; that is, a few micro-seconds. After the initial, veryrapid potential drop the potential of the fiber is restored by currentflow through the resistance 27 and approaches closely to theappliedpotential after fifty to one hundred microseconds. Due to mechanicalinertia, the fiber remains in contact with the collector longer thanthis period. Therefore, when it returns to its repelled position thecollector rod 20 has been recharged to substantially the same voltageapplied to the electrostatic shield 14. The cycle then repeats. A chargeof 1O- coulombs has been found adequate to recharge the collector rod.

The pulse which occurs on contact of the fiber with the collectorelement is employed in a conventional manner to operate a triggercircuit which in turn controls a suitable recording, transmitting, ortelemetering apparatus, not shown.

The time interval between such pulses vary inversely as the rate ofionization in the ionization chamber, and may range from a count orpulse each half hour to several counts per second. By the use of knownsources of radioactivity, the ionization chamber may be calibrated sothat the number of ion charges represented by each output pulse isknown.

The electrostatic shield 14 plays a very important function in that iteliminates, for all practical purposes the effect of change in theapplied voltage or potential, so that the accuracy of the instrument isnot dependent upon the maintenance of a constant voltage supply as longas the supply is above a predetermined threshold value.

The reason for this may be explained as follows:

The fiber 24 is moved away or toward the collector rod by theelectrostatic forces carried by the charges induced in the fiber by allthe conductors near the fiber. In the construction illustrated the onlyeffective neighboring conductors are the shield 14 and the collector 20.The shield 14 almost completely surrounds the fiber and effectivelyshields it electrostatically from any outside potentials. Except duringthe first instant of the recharging operation the shield is at the samepotential as the fiber irrespective of the applied voltage and thereforecannot exert an electromotive force on the fiber. However, the collectorrod 20 does exert an attractive force on the fiber which increases asits potential is lowered below that of the fiber and the shield.

When a critical potential difference between the collector rod 20 andthe fiber obtains, the force is large enough to attract the fiber intocontact. The critical potential difference is determined by themechanical characteristics of the fiber and thus remains constant. Asthe force which attracts the fiber to the collector is due to thepotential difference therebetween rather than the obsolute potential ofthe fiber and shield, change in the value of the charging voltage, abovea threshold value has no appreciable effect. This is illustrated in thegraph, Figure 6.

After the potential has exceeded a certain threshold value, which .isindicated in the graph at less than fifty volts, further change involtage has only the slightest effect on the change in time between thedischarges. In

4 fact the change in interval may be in the order of 0.005 percent pervolt change in potential.

This is highly important in view of the fact that devices of thischaracter may be employed for long periods of time or used underconditions where the voltage may not be held at constant level.

Having thus described certain embodiments and applications of ourinvention, we do not desire to be limited, but intend to claim allnovelty inherent in the appended claims.

We claim:

1. An automatic ionization chamber, comprising: a sealed envelope, afirst shield extending into said envelope and maintained at the samepotential as said envelope; a second shield disposed within said firstshield and insulated therefrom; an ion collector extending from withinsaid second shield into said envelope, there being accommodationapertures in said shields to clear said collector; a charging elementwithin said second shield and tending to move away from said ioncollector when their potentials are the same and to move into contactwith said ion collector when a predetermined potential diiferencetherebetween occurs; and a source of electrical potential connected withsaid charging element and with said second shield for maintaining thecharging element and second shield at substantially the same potential.

2. An automatic ionization chamber, comprising: a sealed envelope, afirst shield extending into said envelope and maintained at the samepotential as said envelope; a second shield disposed within said firstshield and insulated therefrom; an ion collector extending from withinsaid second shield into said envelope, there being accommodationapertures in said shields to clear said collector; a charging elementwithin said second shield and tending to move away from said ioncollector when their potentials are the same and to move into contactwith said ion collector when a predetermined potential differencetherebetween occurs; a sourec of electrical potential connected withsaid charging element and with said second shield for maintaining thecharging element and second shield at substantially the same potential;and means for transmitting a signal each time contact is made betweensaid ion collector and said charging element.

3. An automatic ionization chamber, comprising: a sealed envelope; afirst shield extending into said envelope and maintained at the samepotential as said envelope; a second shield disposed within said firstshield and insulated therefrom; an ion collector extending from withinsaid second shield into said envelope, there being accommodationapertures in said shields to clear said collector; a charging elementwithin said second shield and tending to move away from said ioncollector when their potentials are the same and to move into contactwith said ion collector when a predetermined potential differencetherebetween occurs; means for maintaining a potential on said chargingelement and second shield above a predetermined threshold value wherebychange in said potential above said value does not appreciably affectthe period between contact of said charging element and ion collector;and means for transmitting a pulse each time contact is made betweensaid ion collector and said charging element.

4. An automatic ionization chamber, comprising: an envelope having aconductive surface; an ion collector therein; means for periodicallyrecharging said ion collector; an inner and an outer shield within saidenvelope and surrounding said recharging means and a portion of said ioncollector, the outer shield being grounded to said envelope, the innershield being insulated therefrom; and means for maintaining saidrecharging means and said, inner shield at substantially the samepotential.

, .5. An automatic ionization chamber, comprising: an

References Cited in the file of this patent UNITED STATES PATENTSVictoreen Nov. 6, 1951 Neher Nov. 4, 1952 Keyes July 17, 1956 Borzin May20, 1958

